The objective of this program project is to improve our understanding of the hormonal regulation of reproductive tissues by elucidating the nature and function of steroid receptors and other hormone responsive proteins. The collaborative research program will consist of 4 individual projects and 3 core laboratories with the following specific aims: 1. To purify and determine the structure of the estrogen receptor protein of MCF-7 human breast cancer cells. 2. To purify and characterize progestin receptor from human uterus and to prepare monoclonal antibodies to this receptor. 3. To purify and characterize the androgen receptor from rat prostate and to prepare monoclonal antibodies to this receptor. 4. To identify, characterize, and elucidate the regulation of, endometrial proteins responsive to hormonal modulation. Core laboratories will fulfill the common needs of the above projects for: a. Protein analysis for composition and amino acid sequence (Protein Analysis Core). b. Supply of certain hormone-responsive cells grown in culture; and characterization of monoclonal antibodies (Hybridoma and Cell Culture Core). c. Coordination of projects, core facilities and common services (Administrative Core).